In the past few years, the Internet has become a popular medium for distributing or in some other way transferring works between users. For purposes of this discussion, a work is any piece of art or work product that varies over time and is placed on a medium for distribution. More particularly, a work is a piece of art or work product that is placed in an electronic medium for use and/or distribution. Furthermore, a registered work is a work for which the identity of the work is known. Recently, many web sites have been offering more video works for viewing and transfers to viewers. For example, the web site YouTube.com provides clips of video data that users submit for other viewers to download and view. For purposes of this invention, some of the clips submitted by viewers are a portion of a copyrighted work such as a television show or movie. Owners of copyrighted works are often not compensated by the website owners or the users for the reproduction of the work. Thus, owners of the works seek either to prevent these web sites for providing the clips of their works or receive compensation for reproduction of their works.
Also, as Digital Video Disks (DVDs) have become more popular, the downloading and unauthorized reproduction of video works has become a problem. There is a booming market for pirated or unauthorized reproductions of video works. In the past, makers of DVDs have tried to use encryption and other methods to prevent unauthorized reproduction of the works. However, most of the methods devised to prevent unauthorized use have been overcome or circumvented by hackers. Thus, owners of the works seek ways to either detect the unauthorized work and receive compensation or prevent the reproduction.
In the past, those skilled in the art have made many advances in detecting the identity of audio works. One example, a reliable method for identifying audio works, is given in U.S. Pat. No. 5,918,223 issued to Blum et al. (Blum) which is hereby incorporated by reference as if set forth herewith. In Blum, fingerprints of segments of audio data of an unknown work are generated and compared to fingerprints of data of known works until a match is found. The fingerprints can be one or more of any number of attributes of audio contents. Some examples of audio attributes include, but are not limited to pitch, frequency spectra, and mel-filtered cepstral coefficients. This method is very reliable in identifying audio works.
However, those skilled in the art have yet to find an efficient and reliable method for identifying video works. One method that has proven promising for identifying video works is the use of scene change events. Data for an unknown video work is read and the scene change events are detected. A metric such as the time between events or frames between the events is determined. For purposes of this discussion, a scene change event is one or more empty frames between different colored frames and/or significant changes in the visual between two adjacent frames or significant change in visual content over a small amount of time. Any event may be used as long as detection is easily repeatable. The sequence of metrics between the events of the unknown work are then compared to a list of metrics between events for known works until a sufficient match is made and the unknown work is identified.
There are several problems with the above-identified method of video work identification. The above method of identifying works is reliable when the unidentified work is a direct copy of an identified work. However, this method is not reliable when a copy of the video work is not a direct copy of the video work. For purposes of this discussion, a direct copy is a copy of a work that includes all of the visual data of the copied video work presented in the same manner as created by the owner of the work. Furthermore, an indirect copy is a copy of video work that has the data modified from the original work. Indirect copies can be made in many different manners. Some examples include but are not limited to reformatting of the data, such as from letter box to conventional format; recording the video work in a second medium, such as video taping a movie from a scene at a theater; copying only a portion of the data; noise introduced in the routine broadcasting of the work; format conversions that occur such as telecining, digitizing, compressing, digital-analog-digital re-sampling, keystoning, rotation translation, playback rate changes, and the myriad of other common transformations commonly known in the art.
Typically, an indirect copy has a different video quality from the original work. Thus, some scene change events in an indirect copy may not be detected or other scene change events caused by the copying method may be detected. In addition, because of time scaling and/or playback rate changes, the time between detected events in the original work and the indirect copy may vary. Thus, the list of metrics for the unknown copy is different from the list for the original work and the above-described method may not detect the match.
Thus, those skilled in the art are constantly striving to find a new method that is more reliable for identifying the unidentified work.